Vibratory devices, such as vibratory plows of the type used to dig trenches for cable laying and the like, are typically supported by tractors or other work vehicles which move them along the ground during their operation. Positioning such vibratory devices for use or nonuse and minimizing the problems associated with vibration are principal concerns with such equipment.
Such vibratory devices are usually supported by a vehicle-mounted lifting apparatus of the type having a support for the vibrator, various connecting means between the support and the vehicle, an hydraulic (or other) lift cylinder, and some sort of damping means (such as center-bonded joints or other elastomeric means) at one or more locations along the connecting means to isolate the vibration from the vehicle and/or from the lift cylinder.
Using some sort of vibration damping means between the vibratory device and the lift cylinder is highly advisable. The strong vibration necessary for digging a trench or carrying out other types of field work with a vibratory device can be destructive of certain parts of the lift cylinder. If not properly isolated from the strong vibrations caused by the vibratory device, the lift cylinder can easily become damaged and inoperative.
Examples of equipment of the prior art for vehicle-mounted adjustable support of vibratory devices include those described in U.S. Pat. Nos. 3,618,237 (Davis), 3,363,423 (Davis), 3,746,100 (Hall et al.), and 4,102,403 (Steinberg).
The devices of the prior art have a number of problems and disadvantages. They tend to be quite complex in construction. Some of them require a number of elastomeric pads and bearings in various places to provide sufficient laboratory isolation. Others require a plurality of pivots in order to raise and lower the vibratory attachment. Still others, while providing some vibration damping between the vibratory device and the vehicle, fail to adequately protect the lift cylinder.
Center-bonded joints, sometimes called bonded torsional bushings or elastic torque cushioning elements, have been widely used for vibratory isolation in vehicle-mounted devices for lifting vibratory implements. U.S. Pat. No. 3,618,237 (Davis) is an example. However, such vehicle-mounted lifting devices of the prior art has tended to be extremely complex.
In particular, the connecting means between the support for the vibratory device and the vehicle typically involves a number of mechanical parts arranged in series and/or a plurality of separate principal pivot points along such series of parts. Such complex structures and linkages have been required to provide both the required lifting characteristics and the required vibration damping by center-bonded joints or otherwise.
A need exists for an improved simplified vehicle-mounted lifting apparatus which is easy to understand and operate, but still provides good vibratory isolation for the vehicle and for sensitive lift cylinders.